This invention relates to ball separators for use in ball bearings; and more particularly to molded plastic ball separators having means to minimize ball pockets to ball clearance. The term "ball separator" refers to a component of a ball bearing assembly which is also commonly known by the names "ball retainer" and "bearing cage".
A problem with ball separators which are fabricated from molded plastic such as nylon for example, is that, if the clearance between the wall surfaces of the ball pocket and the ball is too small, the bearing will tend to heat up excessively due to the friction between the ball and the pocket wall surfaces, and consequently reduce lubrication. The bearing temperature may increase by 200.degree. F. for example. Excessive heating creates a particular problem in this type of bearing since the separator material expands much more rapidly with heat than the steel bearing races. The inherent result is that the radial expansion of the separator ring is significantly greater than the radial expansion of the races; and with a small clearance between the separator pockets and balls, this movement of the separator relative to the balls creates binding, and more friction, and more heat thereby aggravating the problem.
A related situation which further aggravates the problem is that where the ball sockets are spherical, the relatively sharp edges of the spherical pockets act to wipe lubricant from the balls; and this inherently results in less lubrication and increased friction. This problem is also further aggravated by the greater radial expansion of the separator relative to the races.
While these problems can be alleviated to some extent by increasing the ball to ball pocket clearance, this produces a relatively loose separator in the ball bearing; and this looseness of the separator may result in separator vibration and resultant noise. This separator noise may raise the overall bearing noise to an unacceptable level, particularly at high speed.
A principal object of this invention therefore is to provide a new and improved ball separator which overcomes the disadvantages of the prior art ball separators as discussed above.
Another object of this invention is to provide an improved molded plastic bearing separator with means to minimize ball to pocket wall surface clearance, and at the same time minimize ball to separator friction.
A further object of this invention is to provide an improved ball separator to minimize separator noise due to looseness of the separator, and to minimize heat buildup due to bearing to separator friction.
Still another object of this invention is to provide a molded plastic ball separator having pocket wall surface projections defining the ball engaging surfaces of the ball pockets.
These objects are accomplished in a ball separator for use in a ball bearing which includes an outer race, an inner race, and a plurality of spherical balls coacting with these races. The ball separator includes an annular base, and a plurality of annularly spaced fingers projecting generally axially from the base to define individual annularly spaced ball pockets. The ball separator has inner and outer side walls, and is configured to be received between the inner and outer races with its side walls confronting respective races. Each of the ball pockets is formed to partially enclose a respective ball, and has wall surfaces with an effective diameter larger than the diameter of a bearing ball, thereby providing clearance space between the pocket wall and the bearing ball. Each of the pocket wall surfaces has integral projections formed thereon which define ball engaging surfaces having an effective diameter slightly larger than the diameter of the ball to provide a small clearance between the projections and the ball.
More particularly, the projections for each pocket may comprise a plurality of ribs circumambienting the pocket and generally parallel with the separator side walls, a plurality of ribs traversing the wall surface of the pocket either substantially perpendicular to the separator side walls or inclined relative thereto, a plurality of relatively small pads which may be generally cylindrical in shape or dome-shaped, combinations of such ribs and pads, or traversing angled ribs which intersect one another to define lubricant retaining recesses in the wall surface.
Also more particularly the pocket wall surface may be cylindrical, being formed about a generally radial axis of the separator, or the surface may be spherical.
The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawings.